Question: If $x \bigtriangleup y = 6x+y$ and $x \boxdot y = x^{2}+2y^{2}$, find $4 \boxdot (-1 \bigtriangleup 5)$.
Explanation: First, find $-1 \bigtriangleup 5$ $ -1 \bigtriangleup 5 = (6)(-1)+5$ $ \hphantom{-1 \bigtriangleup 5} = -1$ Now, find $4 \boxdot -1$ $ 4 \boxdot -1 = 4^{2}+2(-1)^{2}$ $ \hphantom{4 \boxdot -1} = 18$.